High voltage motorsTroubleshooting Guide: A Comprehensive Guide to Vibration, Temperature Rise, and Insulation Breakdown

When a high-voltage motor fails, production downtime at a factory often results in losses amounting to tens of thousands of yuan per hour. Establishing fault diagnosis capabilities in advance allows for rapid identification of problems when early warning signs appear, thereby minimizing losses. This manual was prepared by Xi'anTaifu Simo MotorCompiled by the Group’s team of maintenance engineers, this document covers the three most common types of failures—excessive vibration, abnormal temperature rise, and insulation faults—and includes on-site diagnostic methods and recommended actions.

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Category 1: Faults Caused by Excessive Vibration

Vibration is the most straightforward indicator of a high-voltage motor’s health. According to GB/T 10068, the root-mean-square (RMS) value of vibration velocity for high-voltage motors during no-load operation must not exceed 2.8 mm/s (Class A) or 4.5 mm/s (Class B). Any values exceeding these standards require immediate investigation.

1.1 Unbalanced Vibration

Fault Characteristics:The vibration frequency equals the motor's rotational speed frequency (1X); horizontal vibration is greater than vertical vibration; bearing temperature is normal.

Common Causes:

• Rotor mass imbalance (due to manufacturing errors or failure to rebalance after maintenance)
• Asymmetrical rotor windings (broken strands or localized short circuits)
• Uneven scaling on the fan blades
• Coupling Installation Misalignment

On-site Assessment:When collecting time-domain and frequency-domain data using a vibration meter, if the 1X component is dominant (accounting for more than 50% of the total vibration), an imbalance can be preliminarily determined. After shutting down the machine, clean the fan and check the rotor for loose parts; if possible, perform on-site dynamic balancing.

1.2 Misalignment-Induced Vibration

Fault Characteristics:The vibration frequency is primarily at 2X (twice the rotational speed), with noticeable axial vibration; the bearings at both ends vibrate in opposite directions.

Common Causes:

• Misalignment between the motor and the load (angular misalignment or parallel misalignment)
• Loose motor mounting bolts caused the motor to shift
• Changes in alignment caused by foundation settlement or thermal deformation

Disposal Method:After shutting down the machine, use a dial indicator to check the coupling alignment. The radial runout must be ≤0.05 mm, and the axial deviation must be ≤0.05 mm/100 mm. After realigning the coupling, tighten the foot bolts; use shims to adjust the height if necessary.

1.3 Vibration Caused by Bearing Failure

Fault Characteristics:Vibration frequencies contain high-frequency components (typically several to several dozen times higher than the rotational speed), resulting in increased bearing temperatures and abnormal operating noise.

Reference for Bearing Failure Rates (4-pole motor, 1,480 rpm):

• Outer ring failure frequency: approximately 180–250 Hz
• Inner ring failure frequency: approximately 250–350 Hz
• Rolling element failure frequency: approximately 120–180 Hz

Recommendations for Action:Once a bearing exhibits characteristic failure frequencies, it should be replaced during the next scheduled shutdown. Operating the unit with a faulty bearing is not recommended, as bearing failure could cause the rotor to strike the casing, resulting in significant damage.Simo motorsThe main high-voltage product lines use standard bearings from SKF or NSK,Parts Lookup PageYou can find the corresponding bearing model.

Category 2: Abnormal Temperature Rise Faults

The temperature of a high-voltage motor winding is the most critical indicator of its health. For motors with Class F insulation, the temperature rise limit is 105 K (the winding temperature must not exceed 145°C at an ambient temperature of 40°C). For every 10°C increase in temperature above this limit, the insulation life is reduced by approximately half (Arrhenius’s law).

2.1 Temperature Rise Caused by Overload

Method of Determination:Measure the three-phase current of the motor and compare it to the rated current on the nameplate. If the current exceeds the rated value by 10% or more and the motor has been running for an extended period, it can be determined that the motor is overloaded.

Troubleshooting:

• The actual power consumption of the load exceeds the design value (due to changes in operating conditions, pipe blockages, pump wear, etc.)
• Drivetrain malfunctions increase resistance (seized bearings, coupling issues)
• The supply voltage is too low (more than 5% below the rated value), causing the current to increase.

2.2 Temperature Rise Caused by Cooling System Failure

IC411 Fully Enclosed Air-Cooled Motor (Most Common Cooling Method):

• Check that the external fan is rotating in the correct direction (cooling performance decreases significantly if it is rotating in the opposite direction).
• Check whether the heat dissipation fins on the housing are clogged with dust (clean them regularly, at intervals of no more than 6 months).
• Check that the fan blades are intact and free of cracks.

IC611 Duct Ventilation Motor (Commonly Used in High-Power, High-Voltage Motors):

• Check whether the inlet air temperature exceeds 40°C
• Check the cooling air ducts for air leaks or blockages
• Check whether the airflow of the cooling fan meets the design requirements.

2.3 Temperature Rise Caused by Three-Phase Current Imbalance

Criteria:A three-phase current imbalance exceeding 5% is considered abnormal; if it exceeds 10%, immediate action must be taken.

Formula for calculating imbalance:Unbalance (%) = (Maximum Deviation ÷ Three-Phase Average) × 100%

Common Causes and Solutions:

• Three-phase voltage imbalance in the power supply: Check the power supply system and contact the power utility for resolution.
• Inter-turn short circuit in the winding: The unit must be disassembled for inspection; in severe cases, the winding must be rewound.
• Poor connection in the junction box: Inspect and tighten the terminals; remove any oxidation.

Category 3: Insulation Faults

Insulation failures are the most serious type of failure in high-voltage motors; if not handled properly, they can lead to ground faults, equipment damage, or even personal injury.

3.1 Specifications for Insulation Resistance Measurement

Regularly measuring insulation resistance is the most effective way to prevent insulation failures:

• Measuring Instruments:Use a 5,000-volt megohmmeter for motors rated at 10 kV or higher; use a 2,500-volt megohmmeter for 6 kV motors.
• When to Take the Measurement:Before each startup (after the unit has been shut down for more than 48 hours) and every six months
• Passing Criteria:The insulation resistance (MΩ) value shall not be less than the motor’s rated voltage (kV) × 1000; that is, the insulation resistance of a 6-kV motor shall not be less than 6 MΩ.
• Absorption ratio:The R60/R15 ratio should be greater than 1.3 (at room temperature); if it is less than 1.3, the insulation condition is questionable.

3.2 Causes of Insulation Deterioration and Remedial Measures

Moisture (the most common cause):

• Symptom: Low insulation resistance; absorption ratio close to 1; even lower after shutdown and cooling
• Treatment: Dry by applying power with no load (keeping the current below the rated value of 60%), or disassemble the unit and dry it in an oven (90–100°C, 8–12 hours).

Dirt Accumulation on Windings:

• Observation: Insulation resistance is low but relatively stable; visible stains are present on the surface.
• Treatment: Clean with a specialized cleaning agent, then dry and apply insulating varnish.

Insulation Aging:

• Symptoms: Insulation resistance decreases year by year, dielectric loss increases, and cracks are visible on the surface of the windings.
• Action: Assess the remaining service life and develop a rewinding plan. Provided by the Xima Motor Repair TeamHigh-Voltage Motor Winding Rewinding Services, On-site inspection and evaluation available

3.3 Partial Discharge Monitoring

Partial discharge (PD) is an early indicator of insulation degradation in high-voltage motors; if left unchecked, it can eventually lead to insulation breakdown. It is recommended that critical high-voltage motors with a power rating of 1,000 kW or higher be equipped with an online partial discharge monitoring system to enable 24-hour continuous monitoring and provide early warning before insulation breakdown occurs.

Recommended Intervals for Preventive Maintenance

• Daily Inspections:Visual Inspection Records for Vibration, Temperature, Noise, and Current
• Monthly:Bearing Lubrication: Re-greasing (Determine the amount of grease based on rotational speed and bearing specifications)
• Every six months:Insulation resistance measurement, terminal tightening, and cleaning of heat dissipation channels
• Every year:Comprehensive shutdown inspection, including measurement of bearing wear, measurement of air gaps, and dielectric loss testing
• Every 3–5 years:Major overhaul, including removal and inspection of the rotor, partial discharge testing of the windings, bearing replacement, and anti-corrosion painting

For more information,Xima High-Voltage Motor Technical Specifications, or contact usQuotation for Motor Procurement and Repair, please feel free to contact the Xima technical team.

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